In an electronic apparatus, such as communication equipment, the amount of generated heat increases as an electronic circuit element becomes faster. Further, the amount of generated heat also increases in a whole housing in which printed circuit boards having high-temperature heat-generating elements mounted thereon are mounted. This requires the electronic apparatus to carry out measures against heat generation, and normally, the electronic apparatus cools the high-temperature heat-generating elements on the printed circuit boards accommodated in the housing, using forced air draft from fans.
FIGS. 18 and 19 illustrate the whole housing. In the housing 100, there are mounted a plurality of subracks 101 each for accommodating a plug-in unit (printed circuit board having electronic circuit elements mounted thereon)
Further, a plurality of fan units 102 are arranged above the subracks 101, for cooling the plug-in units 2 by forced air draft generated by the fan units 102 (the fan units 102 illustrated in FIGS. 18 and 19 are of a type which suctions air upward from below).
Here, in many cases, the plug-in units 2 accommodated in the subracks 101 are not accommodated in all the slots of the subracks 101, and further the accommodated plug-in units 2 are not uniformly arranged, due to the system configuration or the like. In such cases, forced air draft generated by the fan units 102 flows into empty slots having a small ventilation resistance (slots having no plug-in units 2 accommodated therein), which makes it impossible to send sufficient air into the plug-in units 2 accommodated in the subracks 101.
Therefore, to prevent ventilation from being imbalanced, in general, case-like structures called fillers, which serve as dummies of the plug-in units 2, are accommodated in empty slots having no plug-in units 2 mounted therein.
FIGS. 20A and 20B are schematic diagrams of the conventional filler. FIG. 21 is a diagram of openings of the filler. The filler 40 is a structure with a space formed therein, and card levers 40a and 40b for being fitted to the subrack 101 are attached on the front side thereof. Further, open holes 44 as illustrated in FIG. 21 are formed in an upper surface plate 42 and a lower surface plate 43 of the filler 40.
By causing the filler 40 configured as above to be accommodated in an empty one of the slots of the subracks 101, a suitable ventilation resistance is generated (air is also caused to flow into the filler 40 via the open holes 44), and the flow of air through ventilation passages is improved, whereby it is possible to send air not only to plug-in units 2 already accommodated in the subracks 101 but also to other subracks 101 mounted in multiple stages in the housing, and cool them.
As the related art, there has been proposed a technique for enhancing the cooling efficiency and prevention of electromagnetic interferences of a housing by attaching, when a package is not inserted in an opening of a rack, a dummy surface plate to the opening to close the opening with the dummy surface plate, and freeing, when a package is to be inserted, the opening to enable insertion of the package, (see Japanese Laid-Open Patent Publication No. 08-255989 (Paragraph numbers [0019] to [0023], and FIG. 1).
Recently, electronic circuit elements become even higher in the speed of signal processing and come to generate even higher temperature heat. In addition, the packaging density of electronic circuit elements on plug-in units has increased. This requires a higher cooling performance than before.
In the conventional filler 40, the shape and the number of the open holes 44 are fixed, whereby it has been impossible to flexibly change the ventilation resistance generated by the filler 40. Therefore, when the relationship between the ventilation resistance of the filler 40 and that of the plug-in unit 2 mounted in the subrack 101 (which is proportional to the packaging density of electronic circuit elements) is, for example, such that the ventilation resistance of the plug-in unit 2 is larger than that of the filler 40, air is guided to the filler 40, whereby it is impossible to effectively send air into the plug-in unit 2 (even when the fillers 40 are accommodated in the empty slots of the subrack 101, if the packaging density of electronic circuit elements on a plug-in unit 2 is high and the ventilation resistance of each filler 40 becomes smaller than that of the plug-in unit 2, a ventilation passage is formed on the side of the filler 40, whereby it becomes impossible to send sufficient air into the plug-in unit 2).
Further, if expansion of specifications is performed when the system is in operation and a plug-in unit 2 is to be mounted in an empty slot having the filler 40 mounted therein, the filler 40 is pulled out and the plug-in unit 2 is mounted in place. The filler 40 pulled out becomes useless and is discarded. This means that the cost of the filler 40 that is not used in the future is produced, resulting in increased costs of the whole electronic apparatus and degraded customer convenience.